The role of cadmium binding protein, metallothionein, in the pathology of environmental cadmium exposure is a question of prime importance. Although some properties of the protein are known, in-depth studies have not been done to define the metal-ligand structure and dynamics of this protein, their possible role in cadmium movements and deposition in cells, and the actual, quantitative relationship of cadmium binding in the metallothionein to cellular and organismic toxicity from the metal. The present research proposal sets forth a series of experiments which will address these areas of needed inquiry: (1) a variety of physico-chemical techniques including laser Raman and 13C NMR spectroscopy, amperometric titrimetry, and functional group modification will be used to examine the structure of the metal binding sites in metallothionein; (2) kinetic studies will determine rates of metal exchange between metallothionein and metal complexes and ligands; (3) quantitative analysis of cadmium distribution between metallothionein and other cellular constituents will be undertaken under controlled conditions of exposure of rats to toxic and essential metals which produce definite toxic effects.